IMAGE: Three band-tailed pigeons perch in Santa Barbara County. Researchers at UC Davis and the California Department of Fish and Wildlife have identified trichomonosis as a key factor in winter die-offs...
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Credit: Courtesy Dianne Ricky

A new pathogen has been discovered by scientists investigating major
die-offs of pigeons native to North America, according to studies led
by the University of California, Davis, and the California Department
of Fish and Wildlife.

Scientists were able to implicate this new parasite, along with the
ancient parasite Trichomonas gallinae, in the recent deaths of
thousands of Pacific Coast band-tailed pigeons. The die-offs occurred
during multiple epidemics in California's Central Coast and Sierra
Nevada mountain ranges. Scientists named the new pathogen Trichomonas
stableri.

Avian trichomonosis is an emerging and potentially fatal disease that
creates severe lesions that can block the esophagus, ultimately
preventing the bird from eating or drinking, or the trachea, leading
to suffocation. The disease may date back to when dinosaurs roamed
the earth, as lesions indicative of trichomonosis were found recently
in T-Rex skeletons. The disease may also have contributed to the
decline of the passenger pigeon, whose extinction occurred exactly
100 years ago.

Epidemics of the disease can result in the death of thousands of
birds in a short amount of time. An outbreak in Carmel Valley killed
an estimated 43,000 birds in 2007.

"The same parasite species that killed band-tailed pigeons during the
outbreaks were also killing the birds when there weren't outbreaks,"
said lead author Yvette Girard, a postdoctoral scholar with the
Wildlife Health Center in the UC Davis School of Veterinary Medicine
at the time of the studies. "This indicates there may be other
factors at play in the die-offs."

"We are now investigating what triggers these die-offs, which may be
caused by the congregation of infected and vulnerable birds during
certain environmental conditions, or even spillover from another
nearby species," said principal investigator Christine Johnson, a
professor with the UC Davis Wildlife Health Center.

Between winter 2011 and spring 2012, there were eight mortality
events -- defined as more than five dead birds found in the same
geographic area during the same time frame. The study said
trichomonosis was confirmed in 96 percent of dead, sick or dying
birds examined at seven of the mortality events. This disease was
also found in:

36 percent of band-tailed pigeons at wildlife rehabilitation centers

11 percent of hunter-killed band-tailed pigeons

4 percent of the birds caught live and released

"What makes this disease more troublesome for band-tailed pigeons is
their low reproductive rate -- about one chick per year -- and also
that these events are occurring in the wintertime," said co-author
Krysta Rogers, an environmental scientist with the California
Department of Fish and Wildlife. "That means almost all the birds
we're losing during events are adult birds. They're being killed
before they have the ability to reproduce in the spring."

Mortality events in band-tailed pigeons have been reported in
California at least since 1945, but have increased during the last
decade, with outbreaks reported in six of the last 10 years.

"Going into the study, we expected to find a single, highly virulent
species of Trichomonas in birds sampled at outbreaks," Girard said.
"Having two species killing birds at these large-scale mortality
events is surprising."

Necropsies of the birds were conducted at the California Animal
Health and Food Safety Laboratory at UC Davis and the Wildlife
Investigations Laboratory at the California Department of Fish and
Wildlife.

Both studies were funded by the California Department of Fish and
Wildlife and the U.S. Fish and Wildlife Service.

The study naming the new species of parasite is published in the
journal International Journal for Parasitology: Parasites and
Wildlife. The study that explains how trichomonosis is affecting the
band-tailed pigeon is published in the journal Infection, Genetics
and Evolution.

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﻿About UC Davis

UC Davis is a global community of individuals united to better
humanity and our natural world while seeking solutions to some of our
most pressing challenges. Located near the California state capital,
UC Davis has more than 34,000 students, and the full-time equivalent
of 4,100 faculty and other academics and 17,400 staff. The campus has
an annual research budget of over $750 million, a comprehensive
health system and about two dozen specialized research centers. The
university offers interdisciplinary graduate study and 99
undergraduate majors in four colleges and six professional schools.

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